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Too Much Taper Crimp?

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A friend of mine is getting into reloading and is using me as one of his "gurus." (His first mistake!) :P He asked me if you can crimp a .40 or .45 too much? I confess, I don't really know how to answer other than, "it depends!" :(

Anyone have any guidelines I can pass on to him?

Thanks,

Mike

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Yes, you can overcrimp...

The object is to prevent bullet setback during recoil, and to provide sufficient resistence during ignition to allow complete burning of the powder...

I don;t know if there are tables which show the correct amount of crimp per caliber, but for .45 LSWC, I crimp to .470 and with jacketed .45 stuff to .471

Hope this helps..

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As I understand it, overcrimping can cause bullet deformation, and can cut through thin plating or jacketing, and result in bullet fragmentation in flight - though you probably have to crimp the living heck out of it to get there. Both of those cartridges headspace on the case mouth - if you were to way overcrimp (so the case mouth is down inside the bullet), it might result in a headspace problem, too...

FWIW - I have three different factory .40 loads in front of me. Crimps and OALs are:

Win White Box 165gr - crimp .413 OAL 1.113

Rem UMC 180gr - crimp .421 OAL 1.122

Fed Amer Eagle 180gr - crimp .421 OAL 1.124

I measured the Winchester stuff 3 times - it's really crimped that tight. You can see the crimp w/ naked eye, whereas the other two don't visibly appear to be crimped. This same Winchester stuff seems to suffer from setback in my pistol, if it's involved in a jam.

The rule of thumb seems to be roughly .02 over the diameter of the bullet (most case walls are around .01 thick at the mouth.

Here are some nice cartridge drawings of both - it appears the spec for .40 is .423, and .45 is .473.

.40 S&W cartridge drawing

.45 ACP cartridge drawing

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All that you want to do is take the flare from the powder station out of the case mouth. Make the case straight again and don't do any more. Over crimping can be disasterous.

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Most of the .40 cases I have used seem to be .420 OD, and I crimp at .418. I have ran about 15000 of those rounds with great results. Every time I chrono'd it, it was very consistent. There is a thread on this forum somewhere where BE and others recommend crimp for .40, search for it.

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A friend of mine is getting into reloading and is using me as one of his "gurus." (His first mistake!) :P   He asked me if you can crimp a .40 or .45 too much?  I confess, I don't really know how to answer other than, "it depends!"  :(

Anyone have any guidelines I can pass on to him?

Thanks,

Mike

Tell your buddy to get a Lee FCD. It will be the best $12 he will ever spend in this game.

Yes you can over crimp, the answer is not "it depends". Just take the flare out. Any more than that is too much.

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Have your buddy load a round and pull the bullet. Look at the bullet and if there is more than a slight line around the bullet, it is probably too much. Especially with plated bullets. No line at all is best.

Also, if he has to wack the bullet puller more than once, that is another sign of too much.

I'll measure the diameter of the bullet and the thickness of the case wall in two spots and add this dimensions together to get an idea of a no crimp value. From there, measure the OAL, moderately press the loaded round on your bench with your thumb (bullet against the bench) and see if the OAL decreases. If the OAL decreases, reduce your crimp dimension by .002 or so and try again.

Bullets seem to fly best with little or no crimp. Neck tension is what you really need.

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My understanding is that the main use of aggressive crimping of the case rim into a cannelured bullet is in heavy recoiling, heavy bullet revolver cartridges, where the bullets in the remaining rounds might be partly pulled because of inertia ("set forward"?) and so bind the cylinder. This isn't as much an issue in semiautos, unless the COL increases to the point where the round won't feed, or decreases because the bullet sets back a lot on hitting the feed ramp, causing an internal ballistics change because of the change in case volume (possible kaboom).

I think that the main tension holding the bullet in place comes not from the case mouth, but from that part of the length of case which is binding against the bearing surface of the bullet inside the case proper - neck tension, as SRT Driver put it.

I've been told that crimping to the point of leaving a mark on a jacketed bullet runs the risk of separating the lead core from the jacket, which makes for poor accuracy.

All that being said, what seems reasonable to me is to shoot for the SAAMI spec case mouth diameter of the loaded cartridge that you should be able to find in any good loading book (0.423", for the 40 S&W, which I know by heart).

FWIW,

Kevin

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For what it's worth, my gunsmith told me to pull a bullet and make sure of a .003 depth crimp ring on the bullet. I have trouble measuring a loaded round at the crimp. So I just pull it. It seems to be a more accurate way to measure.

I experienced jams on my .45 without a crimp. And we all know, it only takes one to screw your stage. :(

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Yes you can have too much but that's a lot more rare than not enough. I like to pull a bullet and see a ring. I also measure a round and hold it by the rim and lean into the bench pushing on the bullet nose, remeasure, if you can't setback your bullet neither can your gun. That's what you are trying to prevent.

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Thank you all for your answers. I've sent the link to this thread to my friend and he's learning (aren't we all).

And maybe he'll join in? :D

Mike

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Well, he didn't join the group, but he did ask me about overpressure and over-crimping. Here's what I sent him.

If you figure a .40 cal bullet with about 33000psi, the force generated on the bullet's base is about 4100# (F=PA). Would a crimp have a significant effect on this? My intuition says, no.

So how much is "too much" and what are the downsides of "a lot?"

1. Overpressure with catastrophic results. I don't think this is likely.

2. Overpressure with reduced case life. I don't think so.

3. Reduced case life due to "working" the case mouth too many times. More probable.

4. Reduced accuracy. Maybe. Even probably.

And what would be the problems of "not enough?"

A. Bullet jammed into case generating overpressure with catastrophic results. Very possible, esp. in .40 cal.

B. Bullet jammed into case with other "bad but not dangerous things" (reduced accuracy, or ?)

C. Or ??

I'll confess that I don't really see the that #1 would happen, and #2, #3 and #4 could be corrected.

FWIW, I use a Lee FCD on .40, .45 and 10mm. I also do a "thumb press" test by trying to push a bullet into the case of a reloaded round w/o powder or primer (put the cartridge on the table, bullet down, and push on the base of the case as hard as I can).

So, folks, when does "too much" become unsafe, or does it?

Sorry to ramble. :wacko:

Mike

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So, folks, when does "too much" become unsafe, or does it?

Sorry to ramble. :wacko:

Mike

When you start to see pressure signs, back off.

I don't think it is worthwhile to try and come up with a "formula". Just take the bell off the round, and watch the pressure signs as you work up the load (remember, back down, then work up to velocity you want)

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Back in the ol' days, when we didn't have the luxury of crimping as a separate operation, we'd adjust our combination seating/crimping die to remove the flare, hopefully without cramming the case mouth into the bullet too much. Then Mike Dillon came along and built machines that seated and crimped in separate stations! Wow - crazy stuff. And then he even started making dies that crimped auto-pistol cartridges correctly, that is to say didn't actually "crimp" at all, but simply removed the flare from the case, laying the (flared) case mouth perfectly flat against the bullet.

Unfortunately, somewhere during the taper crimp die's evolution (from the roll crimp die), no one bothered to rename it so as to not mislead folks, for generations.

Roll crimping should do just what the name implies - the case mouth is slightly (or sometimes drastically, in the case of a heavy recoiling revolver) rolled into the bullet's cannelure. Which helps prevent the bullet (in the unfired rounds) from moving forward in the case in a revolver. Since revolvers typically headspace on the rim, as long as the roll crimp doesn't deform the bullet's bearing surface, no harm is done with even a heavy roll crimp.

Since autoloaders headspace on the case mouth, however, the case mouth should never be crimped so that the case mouth penetrates into the bearing surface of the bullet. So in the case of an autoloading pistol, the "taper crimp die" should never actually crimp the case mouth into the bullet in any way whatsoever. The roll of the taper crimp die is to remove the flare previously applied to the case (in order to seat the bullet without shaving copper/lead) - returning the case mouth so that is snug down on the bullet, but not crimping the case mouth into the bullet at all.

After some experience one can learn to "see" (without tools) if this has been done correctly. (Either too much or too little.) But until then a good set of calipers will guide you as you adjust the "Flare Removing" die. Using the thin part of the calipers (near the tip), measure the loaded, flare-removed round's case mouth at the very end of the case. The result should be the sum of the bullet's diameter plus 2 times the case mouth's thickness. (Usually .010" for most cases. So in the 40 S&W, the Flare Removing measurement should be approx. .420". Or at the tightest, .419". And be sure to "roll the case mouth around," so you don't just measure it in one spot.

Actually (taper) crimping the case mouth into the bullet almost always results in a loss of accuracy. Not removing the flare enough results in malfunctions. Some gunsmith's will recommend "taper crimping" more than what was previously recommended, and that is easy to understand as to why.

If you remove the flare precisely as outlined as above and your pistol (still) has any sort of feeding malfunctions, I can say for sure that crimping the case mouth more is not the solution. Once I learned how to properly set this dimension, I never experienced any malfunctions due to not enough "taper crimp" in over 20+ years of shooting 20-40,000 rounds/year.

be

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And I crimped my minor nines and now my major nines Smooooooooth. can hardky feel the case mouth........So go figure.

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If you do a (thread's title) search for the word

crimp

you'll find plenty of interesting reading.

Back in the ol' days, when we didn't have the luxury of crimping as a separate operation, we'd adjust our combination seating/crimping die to remove the flare, hopefully without cramming the case mouth into the bullet too much. Then Mike Dillon came along and built machines that seated and crimped in separate stations! Wow - crazy stuff. And then he even started making dies that crimped auto-pistol cartridges correctly, that is to say didn't actually "crimp" at all, but simply removed the flare from the case, laying the (flared) case mouth perfectly flat against the bullet.

Unfortunately, somewhere during the taper crimp die's evolution (from the roll crimp die), no one bothered to rename it so as to not mislead folks, for generations.

Roll crimping should do just what the name implies - the case mouth is slightly (or sometimes drastically, in the case of a heavy recoiling revolver) rolled into the bullet's cannelure. Which helps prevent the bullet (in the unfired rounds) from moving forward in the case in a revolver. Since revolvers typically headspace on the rim, as long as the roll crimp doesn't deform the bullet's bearing surface, no harm is done with even a heavy roll crimp.

Since autoloaders headspace on the case mouth, however, the case mouth should never be crimped so that the case mouth penetrates into the bearing surface of the bullet. So in the case of an autoloading pistol, the "taper crimp die" should never actually crimp the case mouth into the bullet in any way whatsoever. The roll of the taper crimp die is to remove the flare previously applied to the case (in order to seat the bullet without shaving copper/lead) - returning the case mouth so that is snug down on the bullet, but not crimping the case mouth into the bullet at all.

After some experience one can learn to "see" (without tools) if this has been done correctly. (Either too much or too little.) But until then a good set of calipers will guide you as you adjust the "Flare Removing" die. Using the thin part of the calipers (near the tip), measure the loaded, flare-removed round's case mouth at the very end of the case. The result should be the sum of the bullet's diameter plus 2 times the case mouth's thickness. (Usually .010" for most cases. So in the 40 S&W, the Flare Removing measurement should be approx. .420". Or at the tightest, .419". And be sure to "roll the case mouth around," so you don't just measure it in one spot.

Actually (taper) crimping the case mouth into the bullet almost always results in a loss of accuracy. Not removing the flare enough results in malfunctions. Some gunsmith's will recommend "taper crimping" more than what was previously recommended, and that is easy to understand as to why.

If you remove the flare precisely as outlined as above and your pistol (still) has any sort of feedig malfunctions, I can say for sure that crimping the case mouth more is not the solution. Once I learned how to properly set this dimension, I never experienced any malfunctions due to not enough "taper crimp" in over 20+ years of shooting 20-40,000 rounds/year.

be

Some BE shooters would argue that the proper crimp into the lead does indeed help accuracy at 50 yards. I typically crimp into LSWC to .465. I even crimp a bite into the FMJ hardball by .002. My tests on the Ransom show that it is consistant and more accurate this way.

Im not arguing the crimp, just pointing out that there is other information out there.

BE

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The Lee FCD can apparently not (according to the instructions that come with it) overcrimp. I suppose that is all based on not having excessively oversized bullets, and / or thick brass, but I suppose that the idea is that the dimensions will not reduce the diameter so much that you can no longer headspace on the case mouth.

In my experience accuracy is determined by so many factors that the discussion is probably far beyond my knowledge and experience, but for example with certain loads and slower burning powders you want crimp to ensure that you get proper ignition of the powder - heavier crimp will reduce unburnt powder in some of those cases (I've experienced that myself with magnum revolvers - I have no experience with .38 Super, 9X23 etc.) and therefore improve shot to shot consistency. The idea here is to increase case neck tension.

It's also suggested that with really fast burning poweder and a lot of unoccupied (air space) in the loaded case crimp achieves the same. I have no experience of that either, but recall seeing it in a loading manual as a teenager, using 38 spl wadcutter laods as a test.

I've also seen comments in some of the manuals about crimp asissting in aligning the heel of the bullet more squarely relative to the case mouth after the fact - I'm not so convinced of that one, particulalry in a straight walled case without body taper, but I suppose that the theory is possible.

Just bear in mind that to be really consistent (i.e. achieve consistent neck tension) case length needs to be the same to achieve the same crimp, so does case wall thicknes. Taper crimps are a little more foregiving than roll crimps here, but I don't know of any action shooters who trim to the same case OAL. But I do know a few (@nal? self included?) revolver shooters (and silhouette junkies) who do!

a test on rifles: http://www.accuratereloading.com/crimping.html

A discussion on rifles again: http://yarchive.net/gun/ammo/crimping.html (Bart Bobbit)

The answer is surely to test it for yourself and see - and if you aren't capable of setting up to test accuracy to discern a difference it probably won't make a difference to your performance. Sometimes it is aguable that higher neck tension is desireable, that to my mind is what it is about.

Wim

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Interesting thread........

I've gone back to just taking out the flare and have seen significant improvement in 9mm and 40 S&W mostly with fast powders.

Also of note, I don't even see the need for a crimp die on my 650 set-up as I get .420 in 40 and .378 in 9mm after the seating operation using a Redding Competition Seating Die for whatever reason. I think even most seating dies will at least just take out the flare. So I just screw the crimp die down in it's station till it makes contact with the cartridge and lock it down happy knowing the "fare reversal" as already been applied before arriving there anyway. In this case the Taper crimp die is just filling a hole....and spending money on the FCD is a total waste of both money and the effort it takes to stroke the press with it's significantly greater pull force.

TR

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